Variable transfer directional coupler for microwave energy



June 19. 1956 KlYQ su ETAL 2,751,556

VARIABLE TRANSFER DIRECTIONAL COUPLER FOR MICROWAVE ENERGY Filed Nov. 22, 1950 4 Sheets-Sheet l 1 1 l L 1, J5 JO 1] 5 g 1, $51, .45 call g 2 #5 r @E 3 a $515.45 .Eo |o SEYMOUR B.C0///V ATTO R N EY June 19. 1956 KlYO TOMIYASU ET AL 2,751,556

VARIABLE TRANSFER DIRECTIONAL COUPLER FOR MICROWAVE ENERGY Filed NOV. 22, 1950 4 Sheets-Sheet 2 I I o 60% 100% CFFECT/VE (OMMIIIVICATIO/VHPE/PTURE4 v g z 83 z? ai 6/ Z; 5; I; I 7o 4; :4 5 Z6 73 2 0% g;

INVENTORS K/YO TOM/YASU SEYMOUR B. CO/ /N ATTO RNEY June 19. 1956 KIYO TOMIYASU ETAL VARIABLE TRANSFER DIRECTIONAL COUPLER FOR MICROWAVE ENERGY 4 Sheets-Sheet 3 Filed Nov. 22, 1950 '///II/II////// I///////1 55: i z 35; m w J F 2: .322 53:: 1 1 I mm LEGEND r 7R4N8VER$E E VECTOR, srMm-m/c/a MODE- TRANSl/ERSE E marmanwmnmmumoo:

RESULTINT MAXI RESIILT/l/VT INPUT VOLTAGE VECTOR W a T& N p/m J n i xx w June 19. 1956 KlYO TOMIYASU EFAL VARIABLE TRANSFER DIRECTIONAL COUPLER FOR MICROWAVE ENERGY 4 Sheets-Sheet 4 Filed Nov. 22, 1950 if T52:

INVENTORS K/Yo TOM/Y/QSI/ SEYMOUR B. coH/v BY %F% ATTORNEY/% the energy arriving at utilization device 33 would be increased. Ordinarily, however, for the combined features of directional coupling and variable energy transfer or variable energy division between two output wave guide connections, it is advantageous to arrange the openings. 19 and 21 to be of just suflicient extent for total energy that the extent of register of the openings is readily visualized in therespective views A, B and C of Fig. 3. A calibration scale and index may be provided on or associated with thewave guides 11 and 13, for convenient indication of the 'amountof power diverted to the output end of wave guide 13 relative to the power supplied at .the input end of wave guide 11. The remaining power is transmitted through to the output end (the right-hand 7 end) of wave guide 11. With the openings entirely out of register, as illustrated in Fig. 3A, the total input power is transmitted straight through to the output end of wave guide 11, and as indicated by the index mark 45 over the 5 zero of the scale markings on wave guide 11, no power is transferred into wave guide 13, and hence no power is available at the right-hand end thereof.

. As indicated in Fig. 33, when the relative position of 'one of the wave guides has been shifted to the extent to 'bring about a condition of partial register of the openings, f part of the supplied power will be delivered through the right-hand end of wave guide 11, and part of the supplied 'power will be delivered through the right-hand end of wave guide 13. With the openings registering to an extent corresponding to one-half of the extent required for full power transfer, the supplied power is equally divided between the respective right-hand exit ends of wave guides 11 and 13.

1 When the openings are in full register, as in Fig. 3C, the openings being the optimum length for the wave guide dimensions and the'wavelength of'the supplied energy,

' full transfer is effected, so that the energy entering wave guide 11 at its left-hand end is entirely transferred into 'wave guide 13 and proceeds outward through the right,- hand end thereof.

Assuming no impedance discontinuity at theright-hand end of wave guide 13, there is no energy ent in. the right-hand end of wave guide 13 or there- ,b eyond in the conduit system, some energy would be reflected back'to the leftward therein, and would be en- 7 tirely transferred into wave guide 11 to proceed toward the source 31 coupled thereto.

Unless special means are provided for insuring a substantial zero-impedance condition between the contiguous walls it is necessary that they be maintained under pressure, holding them tightly in contact. Otherwise energy leakage would result, and moreover, the behavior of the transfer system would be somewhat erratic.

An arrangement obviating the direct contact between 'the tw o wave guides is illustrated in Figs. 5, 6;. 7 and 8.

This struc ture comprises a lower wave guide 11' and an upper wave guide 13, arranged generally along the lines of wave guides 11 and 13 of Fig. l, but with their adjacent narrow walls separated by a very narrow gap. A

' choke joint system is provided external of the gap along 'a length appreciably greater than the length of the openings in the wave guides 11 and 13, and a system of mechanicalbearings is provided for maintaining the proper I close spacing between the wave guides '11 and 13 and permitting guided relative longitudinal motion. v I The mechanical supporting system includes a pair of downwardly extending side plates 61 and 63 affixed to the The positions of the If a mismatch condition were presnarrower walls areiopened throughout an appreciable longitudinal extent, the effect is to substantially double sion appreciably greater than the cross dimension of the wave guides 11' and 13'. Near the lower edges of the plates 61 and 63 are provided V-grooves, to form portions of ball races for the bearing system. Corresponding V-grooves are provided in members 65 and 67 attached to the sides of wave guide 11', and further V-grooves for the outer ball races are provided in angle members 69 and 71 which include vertically extending sections parallel to and outwardly disposed from plates 61 and 63, respectively. Four series of hardened balls 73, 75, 77 and 79 are situated in the longitudinal ball races thus provided, for accurately maintaining the relative positions shown in the cross-sectional view of Fig. 6 While permitting freedom of longitudinal movement.

Referring to Figs. 6, 7 and 8, a series of choke tines exemplified by tines 81 are provided alongside wave guide 11'. The tines 81 are downwardly dependent from wave guide 13, and are spaced by a very small dimension fromthe outer wall surface of wave guide 11. These tines are preferably substantially one-quarter wavelength long or very slightly shorter than one-quarter wavelength, their width dimensions being'appreciably smaller than their length and the spacing between successive tines being preferably smaller than their width. A similar row of fines 83 is provided at the opposite side of wave guides 11' and 13'. The features of the choke joint per se, embodying the series of tines arranged generally as above described, are set forth and claimed in application Serial No.

197,063 of Kiyo T omiyasu, filed concurrently herewith,

and entitled Choke Joint System.

If desired, a pointer may be provided on side plate 63, and a scale of relative transfer values for cooperation therewith may be provided on the upper horizontal surface or on the exposed side surface of angle member 71,

attached to wave guide 11'.

The choke joint system 81, 83, by virtue of the high impedance between the open-circuit lower ends of. the tines 81 and 83 and the outer wall surface of wave guide 11' adjacent thereto, produces substantially zero impedance between the adjacent edges of the side walls of wave guides 11' and 13'. By the use of the separate tines rather than a longitudinally extensive sheet of material having the same extent of downward projection,,propagation of energy in the choke region parallel to the longi- V tudinal axes of the guide is substantially suppressedu The theory of operation'which at present is believed properly applicable to the variable transfer directional coupler systems of the present invention involves the consideration of two modes of wave energy propagation which prevail-within; the mutually adjacent wave guide portions whose interiors are exposed to each other through the longitudinally extensive openings in the respective guides. It is customary to design a rectangular wave guide for eflicient transmission of energy of a known frequency, the mode of transmission being a fundamental mode of the guide usually referred to as the TE1,0 mode.

This is the dominant transverse electric mode. The a dimension of the simple rectangular wave guide ordinarily is such as to prevent it from transmitting energy of this frequency in any of the known higher modes.

When two of such wave guides are juxtaposed with their narrower faces mutuallyadjacent, and-the adjacent the a dimensionof the wave guide portion. This wave :guide portion is then capable of supporting energy in two modes of propagation, the first being the simple transverseelectric mode TE1,0 described in connection with verse electric field vectors representing the first of these modes .are illustrated in solid line in Figs. '10A and 10B,

upper wave guide 13', these side plates being vertically disposed and being separated from each other by a dimenand the electric field vectors representing the latter'of these modes arerillustrated in dotted lines in Fig. 108.

Energy introduced through the lower half of thedouble {asymmetric-a1) mode.

pable df exciting both of the modes represented in FOB, the resulting excitation phase being as illustrated by the vector directions in this view. 'It will be "observed that the electric vectors of respective TE1;o and TE2,o modes are cophasal in the lower half of the *elfectively enlarged wave .guide portion, while the phase vectors are mutually opposed in the upper half of the broad wave guide.

Thus, with reference to Figs. 1 and 3, the hold intensity distribution in the lower half of the double-width wave guide portionJ-ustto the right'of the commencement thereof, is such as to have 'strong =e'nergi'za tion in the lower half and very weak energization in the upper half, "the latter due to the phase opposition of the two modes.

Now, if the energy component of the TE1,0 mode illustr ated in solid line in Fig. 103 and the energy component of the TE2,0 mode illustrated in dotted line in this s'a'me view were propagated at equal speeds along the double-width wave guide portion, shown in Fig. 9

extending from station 10-13 to station IO C, the Wave 'ener-gy wou'ld continue to be substantially confined to the lower half of the volume bounded by the abutting side walls of the juxtaposed wave guide structures. But

"the two modes illustrated in Fig. 10B are not propagated at equal velocities, the velocity of propagation of the simple transverse 'elec'tric mode TE'1,'o (the mode characterized by symmetry of the electric vectors) being slower than the phase velocity of propagation of the TEao Accordingly, when the energy has been conveyed an appreciable distance along the inktaposed wave guide portions, the two wave energy components in the lower half of the juxtaposed 'wave guides have progressed toward phase opposition"; Whereas the Wave energy components in the u per half of the guides,

originally in phase opposition, have progressed toward phase addition or phase reenforc'e'ment. Complete "transfor of the energy to the opposite wave guide section -'is achieved by providing communication between the juxta'p'osed wave guides over just the extent necessary for a relative phase shift of 180 between symmetrical and asymmetrical energy transmission modes, as illustrated in Figs. 10B and 10C, such that the phase vectors of the respective transmission modes in the lower half of the juxtaposed wave guides are opposed in the region most remote hour the source -'(i. e. at station IQ-C) and the vectors in the upper portion representing the respective modes of propagation are cophasal. g V

As is apparent, if the openingbetween the two wave guideswere continued. even further, the further phase progression would result in a tendency for the energy to be retransferred to the first wave guide, a doubledlength of the exposed openings being sufiicientto provided complete restoration of energy into thefirst wave :guide sec- ,tion, the rightward direction of energy propagation being maintained throughout.

A basic design of a variable transfer directional coupler involves entirely open narrow walls of the respective wave :guides, wherethey are juxtaposed, so that the eifective wave guide portions thereat has substantially smooth .broad walls and substantially no discontinuity at the junctures along the broad walls. This applies to the preceding discussion of operating principles. Either of two important departures may be made, f or achieving greaterlength of the openings for a complete transfer, or for achieving some foreshorteni-ng of the openings if desired. For

the former purpose, inductance cross-bars may b' e provided across the opening inone of the two wave guides,

' providing effective shun't inductive loading for the TEro inode. Negligible effective loading is thereby provided for the "fl-32,0 mode, because this mode involves subsiinfiall'y zero transverse electric field between "the middle regions of the two broad side walls. With the iii'iub tafice loading, the phase velocity or rue Tlino niece is rnereased, 4 as phase velocity nearer to-equality with the phase velocity of the Tfim mode, thereby requiring a gi'eater 'leng'thiof theopenings for comple-te-iinergy transfer. is desirable many applications, for various purposes, one example "being to provide such "increase of the e'extent of the relative movement as to enable the user to achieve more ease bf adjustment and calibration, or to iprovide more :gradu-ations of the scale.

The opposite 'elfeet may be achieved by the openings narrower than the internal 'crossa'dimension of :the wave guides, i. e., making the openings in the form of elongated narrow slits. "Shunt capacitive loading for the TE1;-d mode is thus accomplished, with the result of decreasing the phase velocity in this mode, andre'latively enlarging the margin of :phase velocity of the TE2,0 :mode or asymmetrical mode energy component ever the phase velocity of 'the "symmetrical inode component. Accord- 'ingly, the length of'the'openingsfor 100% energy transfer is foreshorfened.

The operation of the present variable transfer directional coupler "system may be :better visualized by more detailed reference to Figs; 9., l0 and 11. 'Fig. 9 schematically indicates 'the source 31 supplying energy through wave guide 11 to a utilization device -33 a-ndfor through wave :guide 13 to a-utihz'ation device 35. in this figure,

' the openings of wave guides 11 and 13 are indicated :as

being in full register, for substantially complete energy transfer, and hence for maximum energization of aevree 35 and negligible energization "of :device 33. Fig; 9 serves to indicate not only the cross-sectional Iplanes through the structures corresponding to views A, i3, D and C :of Fig. 10, but also to indicate the "cross-sectional -tplanes cdri'espbnding'to views A'I inclusive in Fig. 11. In 100,- the solid line vectors correspond in all respects "to the solid line vectors shown in Fig. 105-, representing the even or symmetrical or TE'rm .nro'd'e, directed to the rightward'. The dotted line vectors, representing the energy *componerits of the TEz-,o .mode, however, are shown "as 10-13 :in 9 is appreciable, being the vector sum of the =c'ophasal energy components, and substantially no energy is present in the right-hand portion of wave guide-1:1, due to the phase "opposition of the component vectors.

Fig. 11 illustrates this situation in terms or rotating vectors, the positions ef the vectors indicating an instantaneous picture of phase distribution over the region from p'lane 11-A to plane 11-1 in Fig. 9. The input voltage vector is represented .in Fig. 11A as representing the phase "and intensity of energy arriving through wave guide 11 at the plane designated 'll-A in Fig. 9. The energy atft'he next station along the lower wave guide region is indicated as divided between two mode components .as shown in the lower portion of Fig. 11B, one component being indicated in solid line as lagging the vector of 11A by '90 and the other vector being indicated as lagging the :inputveotor by slightly more than The solid vector in the lower circle of Fig. '1 13 represents the T'Em mode energy [in the lower wave guide portion, whereas the dotted vector in the lower circle of 'liB represents the TEznicomp'onent energy therein. The upper vector diagram of Fig. 1113 represents the phases of the TEio energy :component (the solid line vector) in the upper wave guide portion at station ll-B of Fig. 9,"wherea's the dotted line vector represents the mode component in the same wave guide region.

The vectors in the lower portion of Fig. 118 would be cop'hasal, and the vectors in the upper'portion would-be mutu lly opposed, but for the lower phase velocity of "the TE gu mode energy, which results in the lesser phase -FigsrllC, 11D, 11E, 11F, -11G and 11H indicate the relative phase distribution at the correspondingly designated stations in Fig. 9 at the inoment of time chosen for the entire phase examination, the last of these vector diagrams showing that after propagation over anappreciable distance, the componentvectors in the upper wave guide have progressed into a substantial phase additive condition and the component vectors in the lower wave guidehave progressedinto a condition for substantial phase'opposition. Accordingly, as indicated at Fig. 11F, substantially zero resultant energy is propagated on to the right in wave guide 11 toward utilization device ',33, whereas substantially full intensity energy is propagated to the right through waveguide 13toward utilization device 35.

The diagrams in Fig. 10 indicate a distribution of the I solidline VCtOYS-.thCTE1 ,0 electric field vectors-substantially according to a 180 sine wave envelope, and the disposition of the dotted line vectorsfor the TE2,0 com- -ponent substantially according to a 360isine'wave envelope. Hence, it is necessary to. take into account the presence of energy in still higher modes, mainly the TE3,0 mode, in order to satisfy fully the boundary conditions between the wave energies of Figs. 10A and 10B,

and similarly to satisfy fully the boundary conditions between the energy conditions .of Figs. lC.and D. The 180 sine wave envelope distribution of Figs. 10B and 10C correspond to the enlarged wave guide sections thereof, substantially free from concentrated shunt inductive or shunt capacitive loading.

Where concentrated shunt inductive loading is provided, as with cross bars 23 as shown in Fig. 2, and as indicated schematically in Figs. 12B and 120 by the inductance symbols across the middle regions of the enlarged wave guide section, the symmetrical .mode energy is reduced to very low intensityatv the middle region. Accordingly, its absolute values 'of intensity are distributed in substantial correspondence .with the distribution of intensity values of the asymmetrical mode, and so there is less necessity for higher modes to play a part in fulfilling the'boundary condition requirements where inductive loading. is employed.

It is generally desirable to design the variable transfer directional coupler so that in the inter-communicative region the enlarged efiective wave guide is of ample size to support the TE2,0 mode but is of insufficient size to support the TEa,o mode, avoiding the complications which can result from three different modes having three respective phase velocities.

Where the inductance cross-bars are provided in the opening in one'of the wave guides, the latitude in design .of the overall width in the intercoupled guide section for prevention of TE:,0 mode propagation is enhanced.

. It has been pointed out above "that the TEa,n mode is instrumental in satisfying the boundary conditions between the vector pictures of Fig. 10A and Fig. 10B, and

. similarly, between those of Fig. 10C and Fig. 10D., This istrue, even though the composite wave guide section is .so dimensioned as to prevent efiicient transmission of .TE3,0 mode energy, since the higher modes are then present at the entrance and exit boundaries of the composite wave guide secfion, but are evanescent.

For the purpose of maintainingsubstantial continuity of characteristic impedance of each of the two wave guides which together constitute the variable-transfer directional coupler system of the present invention, the greater internaLcross-sectional dimension of each wave guide (its a dimension) is maintained substantially uniform even through the section containing the opening in its narrower wall, as by the provision of an inside plate cor- 7 responding in thickness to the wall, thickness of the wave guide, the plate being attached to thevnarrow wall of the wave'g'uide opposite to the opening. Such a plate 91 is illustrated in Fig. 13; as incorporated in wave guide 13 opposite to the opening 19 therein. No such plate is wave guide sections or devices.

provided in wave guide 11, where the inductance cross bars 23 have their inner surfaces spaced from the lower wall by'a' dimension equal to the spacing betweenthe lower and upper walls of the wave guide.

. .As illustrated in Fig. 14, where a choke coupling sys tem is'employed and there is a slight spacing between the wave guides 11' and 13', the wall 91' is made thicker byan amount equal to the spacing between the wave guides, to maintain uniform total internal height dimensions throughout the wave guide system.

Where no inductance cross bars are employedand there is a continuous openingtas illustrated in Fig. .9, a

plate is provided in each of the wave guides, the plates .91 and 92 respectively compensating for the omission of .end at which to supply energy. Considering Fig. 9, for

example, the energy may be supplied at the left-hand end of wave guide 11,as shown, or at the left-hand end of wave guide 13, or at the right-hand end of either of the guides. This holds true, whether or not inductance cross-bars are provided in the opening of one of the two wave guides.

The inductance cross-bars, when included in the energy transmission path in only one wave guide (the opening in the opposite wave guide being out of register therewith), have so little effect as to leave it substantially immaterial whether the energy be normally transmitted through the guide containing the cross-bars or through the opposite guide.

Throughout the foregoing descriptions, one guide is shown as straight at both ends and the other guide is shown as being curved at both ends. The curved ends are provided merely for clearancefor the end coupling flanges, and for convenience in attachment of further Such curved sections may be provided in either guide or in both guides,

Examples of dimensions and operating frequency of three workable variable transfer directional coupler systems are given below: 7

Width (I. D.) of wave guide: 0.40 inch Height (I. D.) of each wave guide: 0.90 inch width of the wave guides) Length of openings: 8% inches Number of cross-bars: 21

Spacings'between cross bars, center-to-center: 0.375 inch For an operating frequency of 9,000 megacycles per sec.,

cross-bars of 0.040 inch diameter were used.

For an operating frequency of 10,000megacycles per sec.,

' cross-bars of 0.032 inch diameter were used.

Cross-bars of square cross-section, with their width equal to the diameter of round cross-bars, were also found to give good results.

A version without the inductance cross-bars, but with full-width openings, was found to yield the required results at 8,700 megacycles with the following dimens1ons:

Width (I. D.) of wave guide: 0.40 inch Height (I. D.) of each wave guide: 0.90 inch Width of openings: 0.40 inch Overall length of openings: 2.96 inches Length of openings, exclusive of tapered ends: 2.50 inches Couplers for other frequencies may be dimensioned proportionately from the above data, the dimensions being sealed in direct proportion to wavelength. Where a different relation exists between the wave guide dimensions and the wavelength of the energy to be dealt with, allowance must be made for the resulting change in relative phase velocities in the wave guide. .The requiredchanges of dimensions of the coupling openings "are-1,358

or the easier-arise cfo's's bar's, or both, may be determined experimentally, employing the above sets of work i'ng dimensions as starting points.

Changes in -the number of cross-bars per unit length along an opening, or in the widths of the cross-bars, may easily be carried out 'for achieving an effective change of length of a given set of openings. For example, if a variable transfer directional coupler system is :worked out wherein -'the openings are not quite sufiicien'tlyflong for making available the total transfer of energy from the first wave guide to 'the second, fewer cross-bars may be provided, or the cross-sectional dimensions of the cross-bars may be decreased for the increase of the inductive-reactance values. Conversely, if the openings are so long as to permit total energy transfer at a condition of partial register, and this condition is undesirable, the inductance cross-bars may be increased in number or cross-sectional dimensions.

The apparatusof the present invention is readily suited for use a variety of applications .in addition to variabile-transfer directional coupling. -It may be used not only as a variable power divider, as illustrated in Figs. 3A, 3B and 3C, but also as a power combining manifold device readily adjustable to accommodate plural power sources, whether their power contributions are equal or unequal. Considering Fig. 3B, for example, generator 31 could be replaced by a load, and first and second generators could be coupled to the right-hand ends of the respective wave guides. Assuming the proper 90 phase relation maintained between the first and second source outputs, their total combined power is supplied through the left-hand end of wave guide 11.

For equal contributions by these sources, the relative position between guides 11 and 13 is correct as shown in Fig. 3B. If the source coupled to the right-hand end of wave guide 11 supplied a power contribution only onethird as great as the contribution of the source coupled to the right-hand end of wave guide 13, the latter guide would be repositioned to bring index 45 into register with the 0.75 power mark, the mark for the power at the right-hand end of guide 11 being one-fourth the power at the left-hand end thereof, and thus one-third as great as the power at the right-hand end of wave guide 13. One example of two sources with the required fixed phase relations therebetween would be a pair of klystron output amplifiers or klystron output resonators controlled by a common oscillatory energy circuit.

In all of the foregoing versions of the present invention, the wave guides have been described as stacked one above the other, with their narrow walls adjacent and the openings therein. A version of the present invention can be made with two wave guides side by side, i. e. with broad walls mutually adjacent and with their transverse electric field vectors in alignment. In such an arrangement, the openings in the adjacent broad walls are longitudinal as before, and are preferably much narrower than the wall width, e. g. one-tenth to one-fifth the wall width. This type of variable transfer coupler requires a very long region of communication, in general several times as long as required by a coupler wherein the narrow walls are juxtaposed and provided with openings of sufiicient length for complete energy transfer. This type of coupler has very high directivity, but requires precise symmetry of the location of the openings in the broad walls.

This invention is not limited to use with rectangular wave guides of equal sizes. Unequal guides may be used, as may also wave conduits having circular or elliptical cylindrical configuration, or other configurations.

Since many changes could be made in the above construction and many apparently widely diiierent embodiments could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying draw- '10 ings shall be interpreted-as illustrative and *nvin a limitingfsens'e.

Wh'atis claimed is; j

1. Variable microwave energy transmission s isar ams comprising and second wave guides each having a rectangular cross section, -a narrow wall of said sm-wave guide being adjacent to and separated from a narrow wall of said second wave guide, said narrow wall of'said fir's't wave g'uide'having a substantially rectangular longi- 'tudinally extensive apes-mg therein apprecialfly lo er than the width "of said narrow wall of said first are guide, said narrow wall of said second wave guide havi ng a substantially rectangular longitudinally extensive openin therein appr ciably longer than thewidth of said narrow wall er "sa second wave guide, the length or the rectangular longitudinally extensive openi said "nest and second waveguides being at least aqua to that length req red for run ener transfer from use of said wave guides to the other wave guide when said openings are inffull register, one of said adjacent n new walls including a series of spaced inductance or bars across the rectangular longitudinally extensive'i-speiiitig therein, a substantially rectangular plate having a length and width substantially equal to the length and width of said rectangular longitudinally extensive openings and having a thickness substantially equal to the sum of the thickness of the narrow wall of one of said wave guides and the separation between adjacent narrow walls of said first and second wave guides, said rectangular plate being situated within one of said wave guides and extending longitudinally along its narrow inner wall opposite the rectangular longitudinally extensive opening therein, the surface of said plate as measured along its width being contiguous with said opposite narrow wall, and means guiding one of said guides relative to the other for providing longitudinal variation of coupling through the openings in the adjacent walls.

2. Variable microwave energy transmission apparatus comprising first and second wave guides each having rectanguluar cross-section, one wall of said first wave guide being adjacent to and longitudinally movable relative to one wall of said second wave guide, said one wall of said first wave guide having an opening therein appreciably longer than the width of said one wall of said first wave guide, said one wall of said second wave guide having an opening therein appreciably longer than the width of said one wall of said second wave guide, the lengths of said openings in said first and second wave guides being at least equal to that length required for full energy transfer from one of said wave guides to the other wave guide when said openings are in full register, one of said wave guides including a series of spaced inductance cross-bars across the opening therein, and means guiding one of said wave guides relative to the other and retaining said wave guides in alignment for providing longitudinal variation of coupling through the openings in the adjacent walls.

3. Variable microwave energy transmission apparatus as defined in claim 2 wherein both the openings in the adjacent walls of said wave guides are of substantially equal lengths.

4. Variable microwave energy transmission apparatus comprising first and second wave guides, said first wave guide having a first fiat wall portion and said second wave guide having a second fiat wall portion adjacent to and longitudinally movable relative to said first fiat wall portion, said first and second wave guides having first and second longitudinally extensive openings in said first and second flat wall portions, respectively, for microwave energy communication between said first and second wave guides, the lengths of said first and second longitudinally extensive openings in said first and second fiat wall portions being substantially equal to that length required for full energy transfer from one of said wave guides to the other wave guide when said openings are in full register,

one of said wave guides including a series of conductive bars spaced apart and extending transversely across the opening in said flat wall portion, and means for guiding one of said wave guides for longitudinal movement relative to the other of said wave guides for variation of the extent of registry of said openings.

5. Variable microwave energy transmission apparatus as defined in claim 4, wherein said first and second wave guides have rectangular internal cross-sectional outlines,

said first and second wall portions being the mutually.

adjacent narrower'wall portions of the respective wave guides, and said openings being as wide as the internal width dimensions of said first and second wall portions.

6. Variable microwave energy transmission apparatus as defined in claim 5, wherein said first and second mutually adjacent wall portions are spaced apart, said spacing being very small compared to the Width of said adjacent wall portions, said variable microwave energy transmission apparatus including energy leakage suppression means for inhibiting the escape of microwave energy through the space between said first and second fiat wall portions.

I 12 References Cited in the file of this patent UNITED STATES PATENTS 2,418,809 Albersheim Apr. 15, 1947 2,423,526 Sontheimer et al. July 8, 1947 2,496,772 Bradley Feb. 7, 1950 2,519,734 Bethe Aug. 22, 1950 2,541,910 Bangert Feb. 13, 1951 2,575,571 Wheeler Nov. 20, 1951 2,579,327 Lund Dec. 18, 1951 2,657,361 Henning Oct. 27, 1953 OTHER REFERENCES 736 relied on. Copy in 178-44-1F. 

